The present invention relates to novel awn-inhibitor genes of triticale that result in the reduction of awn length and produce an awnless characteristic in a number of different genetic backgrounds and environments. The present invention also relates to a triticale seed, a triticale plant, a triticale cultivar, and a triticale hybrid that contain the awn-inhibitor genes. In addition, the present invention is directed to transferring the awn-inhibitor genes in the triticale plant to other triticale plants, and is useful for producing novel types, cultivars, and hybrids of awnless and short-awn triticale.
Triticale (Triticosecale Wittmack) is a genus of plants created by pollinating wheat with rye, then manipulating the resulting genetic combination so that the combined genomes of the wheat and cereal rye are both retained in subsequent generations. With its genetic endowment from wheat and rye, triticale is a new crop plant that ideally combines the yield and quality advantages of wheat, with the hardiness, pest tolerance, and adaptability of rye.
Researchers began crossing wheat and rye in the late 1800's, but fertile triticales capable of producing viable seed were virtually unknown until after 1938. In that year the Swedish geneticist Arne Muntzing produced fertile triticale by treating wheat-rye crosses with colchicine, which doubled the chromosomes so that normal reproductive pairing and division could occur. With normal pairing and division of chromosomes at meiosis, a triticale could be reproduced through subsequent generations. Triticale became a new crop plant, similar to but distinct from wheat and rye and the other cereal grains in its breeding, seed production, and use. Once created and reproduced, a triticale does not "revert" or "break down" to its wheat and rye components. Triticale is primarily a self-pollinated crop like wheat, although as a result of its rye component it does out-cross more frequently than wheat.
Commercial cultivars of triticale first became available in the 1960's in Europe. Acreage in the U.S. began to grow in the 1980's. Currently worldwide acreage of triticale is approximately 6 million, while that in the U.S. is approximately 450,000. Triticale is managed like wheat, though it requires less inputs such as fertilizer, water, and pesticides.
Most of the triticale now grown in the United States is for grazing and harvested forage (hay and silage) for beef and dairy cattle. Triticale competes with other cereal grains, primarily wheat and oats, for these forage markets. These markets in the U.S. are substantial. Annually in the U.S. over 18 million acres of cereal grains are planted for forage production. In the southern Central Plains alone, over 12 million acres of wheat are used for pasture for grazing on average each year. Cereal silage and hay are important in the major dairy producing regions, and cereal hay is a popular forage for horses.
Compared to wheat and oats, triticale has important advantages for forage production in terms of yield, production costs, and tolerance to pests, drought, low fertility, mineral toxicities, and heavy grazing (National Research Council, Triticale: A Promising Addition to the World's Cereal Grains, National Academy Press, Washington, D.C., 1989.) Despite the important advantages of triticale over other cereal grains for forage, triticale is now planted on less than 3% of the U.S. cereal forage acreage. A major limitation on the use of triticale for forage has been the presence of awns on triticale. Awns are long needle-like appendages on the flower "pike" or "head" located at the top of the plant. As the flower head emerges from the stem and develops through the stages of flowering and grain development, the awns stiffen and become increasingly irritating and injurious to livestock that graze the plants as pasture, or eat the harvested plants as hay. "Rough awns in small grain hay can cause cattle considerable soreness and irritation to the eyes, mouth, lips, gums, and lower surface of the tongue" as described in Watson, S. L., et al., Small Grain Cereals for Forage, Cooperative Extension Service, Kansas State University Publication MF-1072, 1993. Awns can cause injury and infection in livestock, which increase veterinary costs and decrease animal health. Even when injuries do not occur, the presence of awns can reduce feed intake and the profitability of livestock production.
With respect to awns, oats and some wheat cultivars have had an important advantage over triticale. Oats do not have the long, heavy awns that cause problems in pastures or hay. Although some wheat cultivars have awns, others do not. The most popular wheat cultivars for forage production have no awns or very short awns (Carver, B. F., et al., Registration of Three Pairs of Awned vs. Awnleted Near-Isolines of Hard Red Winter Wheat, Crop Science, 33:885, 1993.; Krenzer, G., et al., Wheat Variety Trial Results-1993, Cooperative Extension Service, Oklahoma State University, Department of Agronomy, Publication PT 93-1, 1993; and Weyrich, R. A., et al., Effects of Awn Suppression on Grain Yield and Agronomic Traits in Hard Red Winter Wheat, Crop Science 34:965-969, 1994.)
Although they differ importantly in intraspecies diversity of awn development, wheat and triticale have the same pattern of plant development and morphology, including the development and morphology of heads and awns. The flower heads, or spikes, develop at the top of the main stem and secondary stems called tillers, which are analogous to branches. An individual plant usually has a main stem and multiple tillers, the number of which depends on plant density, soil moisture, nutrient supply, pest damage, seeding date, and temperature, as well as the genetics of the plant. Typically two to four tillers per plant will develop to the point of developing a head, although under conditions of high plant population, stress, or late planting date a plant might have only a main stem. Tillers develop sequentially during growth of the plant. Primary tillers develop one at a time from buds in the crown of the main stem. Secondary tillers may develop from buds in the axils of leaves on primary tillers, and tertiary tillers may develop on secondary tillers. The morphology of an individual tiller, including its awn development, is affected by competition among tillers for light, water, and nutrients, and the environmental conditions under which each tiller initiates and develops. The main stem and each of the tillers develop along a different course of time, and may be exposed to different growing conditions at the stages of growth affecting awn development. The later appearing tillers, however, have fewer leaves so many reach maturity at roughly the same time as the earlier tillers.
Each head at the top of a stem consists of multiple spikelets, each of which consists of multiple florets that produce pollen, ovules, and eventually kernels. Awns are located on bract-like parts of the florets called lemmas. Among wheat cultivars, awn development varies from those essentially lacking awns to those with awns on every lemma exceeding 100 mm. In contrast to wheat, essentially all rye cultivars have awns. Triticale cultivars have awn lengths and frequency exceeding that of the shortest-awned wheat cultivars, perhaps reflecting the influence of its rye genetic component.
Developing a triticale plant having no awns or very short awns, like those of wheat cultivars favored for forage, would provide all of the important benefits of triticale in terms of higher yield, wider adaptability, greater durability, and reduced production inputs, while avoiding the substantial problems associated with awns. With such a triticale, acreage of the crop should increase dramatically, benefiting forage and livestock producers and others involved in the development, production, and use of forages.
Because of these substantial potential benefits, significant plant breeding effort has been directed toward breeding triticale with short or absent awns comparable to those of the wheat cultivars now favored for forage. The most common approach to developing shorter awned triticale has been to use genes responsible for short or absent awns in wheat. The genetics of awn development in wheat is believed to involve the interplay of numerous awn promoter genes (at least thirteen) and three inhibitor genes. In common wheat (Triticum aestivum), the three inhibitor alleles have a dominant effect: when present they largely override the awn-promoter genes at the other loci resulting in significantly shorter and fewer awns.
The awn-inhibitor genes in wheat are called "Hooded", "Tipped 1", and "Tipped 2" (International Wheat Genetics Symposium, Proceedings of the Sixth International Wheat Genetics Symposium, Kyoto, Japan, 1983; Molchan, I. M., et al., Genetics of Awnedness and Varietal Reproduction in Winter Wheat, I. Awnedness as a Quantitative Character, Soviet Genetics 16(2):222-229, 1980; Molchan, I. M., et al., Genetics of Awnedness and Varietal Reproduction in Winter Wheat, II--The Nature of the Dominance of the Degree of Expression of Awns in the Spike, Soviet Genetics 16(3):320-326, 1980; Molchan, I. M., et al., Genetics of Awn Development and Varietal Reproduction in Winter Wheat, III--Nature of Segregation After Crossing of the Forms Differing in Degree of Awn Expression in the Spike, Soviet Genetics 17(10):1211-1216, 1982; and Watkins, A. E., et al., Variation and Genetics of the Awn in Triticum, J. of Genetics XL (1 &2):243-273, 1940.) "Hooded" is of limited commercial significance, and results in short, broad awns that are curved inward into a hood shape. Tipped 1 and 2 account for the absent and reduced awn characteristic that is of commercial importance in wheat. Tipped 1 results in very short or absent awns at the base of the head, while awns increase in length toward the top of the head. Tipped 2 results in uniformly short awns over the entire head. Plants that are homozygous for both Tipped 1 and 2 inhibitor alleles have heads that either have no awns or very short awns depending on promoter genes and modification factors. Plants with the various other combinations of homozygous and heterozygous Tipped 1 and 2 have reduced awns of various lengths, frequencies, and positions on the head (Molchan, I. M., et al., Genetics of Awnedness and Varietal Reproduction in Winter Wheat, I. Awnedness as a Quantitative Character, Soviet Genetics 16(2):222-229, 1980; Molchan, I. M., et al., Genetics of Awnedness and Varietal Reproduction in Winter Wheat, II--The Nature of the Dominance of the Degree of Expression of Awns in the Spike, Soviet Genetics 16(3):320-326, 1980; and Watkins, A. E., et al., Variation and Genetics of the Awn in Triticum, J. of Genetics XL (1 & 2):243-273, 1940.) The Tipped 1 and 2 genes are hereafter referred to in this discussion as the wheat awn-inhibitor genes.
Although the "wheat awn-inhibitor" (WAI) genes are considered dominant, the extent of that dominance, and hence the length and frequency of awns, depends on which inhibitor alleles are present and on the interaction of the inhibitors, promoters, and other endogenous and exogenous modifiers as shown in Table 1. As a result of modified expression of the awn genes in wheat, awn lengths often differ among plants of the same cultivar, heads on the same plant, and even among spikelets on the same head.
TABLE 1 ______________________________________ Factors Determining Awn Length in Wheat ______________________________________ Multiple genes promoting awn development (at least 13 loci) Combination of alleles at these loci establish potential awn development. Wheat awn inhibitor alleles In wheat, three alleles are dominant inhibitors of awn development, and to a large extent override the awn promoters. These three awn inhibitors have a much weaker effect on awn length and frequency in triticale than they do in wheat. Endogenous Factors Regulating Gene Expression for Awns Cytoplasmic modifiers that enhance the effect of awn-inhibitor genes. Factors associated with location of spikelet on head, i.e. basal, mid, apex. Factors associated with location of head on plant, i.e. early, mid, or late tiller. Exogenous Factors Regulating Gene Expression for Awns Drought High temperatures ______________________________________
The complexity and variability of the genetic and environmental basis of awn frequency and length can make description and classification of awnedness difficult and subjective. The term "awnless", for example, has been used imprecisely and diversely in both scientific literature and commercial trade. Some authors have classified as "awnless" any heads that are not fully awned, i.e. that lack the same frequency and length of awns as related fully awned forms (Miller, E. C., et al., A Study of the Morphological Nature and Physiological Functions of the Awns of Winter Wheat, Kansas State College of Agriculture & Applied Science, Technical Bulletin 57, 1944; Molchan, I. M., et al., Genetics of Awnedness and Varietal Reproduction in Winter Wheat, I. Awnedness as a Quantitative Character, Soviet Genetics 16(2):222-229, 1980.) Others have classified as "awnless" only those heads that have no discernable awns, i.e. no lemma extensions exceeding 1 to 2 mm (Bayles, B. B., et al., Classification of Wheat Varieties Grown in the United States in 1949, United States Department of Agriculture Technical Bulletin No. 1083, 1954.) Most authors have adopted a classification for "awnless" heads that is intermediate to these extremes, in many cases using vague, qualitative criteria for their classification (Molchan, I. M., et al., Genetics of Awnedness and Varietal Reproduction in Winter Wheat I. Awnedness as a Quantitative Character, Soviet Genetics 16(2):222-229, 1980; Molchan, I. M., et al., Genetics of Awnedness and Varietal Reproduction in Winter Wheat, II--The Nature of the Dominance of the Degree of Expression of Awns in the Spike, Soviet Genetics 16(3):320-326, 1980; Watkins, A. E., et al., Variation and Genetics of the Awn in Triticum, J. of Genetics XL (1 & 2):243-273, 1940.) In addition to "awnless" and "awned", some classifications include "awnleted" for heads with awns that are reduced but still clearly present, and "apically awnleted" for heads that only have awns on the top spikelets. In commercial trade, the term "beardless" is often used to describe cultivars having short or no awns, while "bearded" is used for those with long awns (Bayles, B. B., et al., Classification of Wheat Varieties Grown in the United States in 1949, United States Department of Agriculture Technical Bulletin No.1083, 1954.)
The confusion and misreporting associated with classification and reference to awn length is exemplified by a research publication from South Dakota State University in 1986 announcing the development of the triticale variety "Marval", with the claim: "Marval is thought to be the only awnless variety of triticale" (J. Leslie, South Dakota Farm & Home Research, vol. 37 (2): p21-22, 1986.) However, the official Registration description issued by the breeders of "Marval" described the variety as "awnletted", indicating that "Awns are 5 to 10 mm long at the base of the spike and 10 to 35 mm long at midspike. Marval's awnletted spike is the primary distinguishing feature when compared to other triticale cultivars." (Cholick, F. A., et al., Registration of `Marval` Triticale, Crop Science, v 28:1031, 1988.)
The publications associated with the release of "Marval" exemplify how the term "awnless" has been used erroneously in published descriptions of grain varieties and plants, and highlight the inherent variability within varieties, plants, and heads in the expression and description of awn lengths, which in the case of "Marval" vary between 5 and 35 mm depending on place on the head and other variables. The emphasis of these publications on awn length also underscores the major significance of awn length for triticale, and the extent and duration of efforts to reduce it in triticale. At the time "Marval" was released, having heads (spikes) with awns no longer than 35 mm was a notable improvement over other triticale varieties, although those heads would not even be classified as semi-awned under currently proposed standards as shown in Table 2.
Classifying plants in terms of awnedness can be even more difficult than classifying individual heads because an individual plant usually has multiple heads, which may differ in terms of their awn length and frequency. The difficulties of classification are compounded further for some cultivars because microenvironmental effects may cause plants of a population of that cultivar to differ in the frequency and length of awns even though they are genetically the same.
Previous attempts to reduce awn length in triticale have involved producing or crossing triticale with wheat cultivars having the WAI ("Wheat Awn Inhibitor") genes. The focus on the WAI genes was logical because triticale originated from wheat and rye, and awn inhibition is common in wheat but virtually nonexistent in rye. In wheat, the WAI genes can result in cultivars for which awns are absent or very short and infrequent. Unfortunately the use of WAI genes or any other factors associated with awn inhibition in wheat have repeatedly and consistently failed to achieve the degree of awn inhibition in triticale that is achievable in wheat. The inadequacy of the WAI genes for triticale may be related to the strong expression of awn development in rye.
In addition to failing to produce a completely awnless triticale, use of the WAI genes has proved to be slow and unpredictable for producing even short-awned cultivars of triticale. To date, the short-awned cultivars of triticale have erratic awn lengths and lower marketability and value than would be true for a product with inhibited awn development comparable to the preferred forage wheats. The failure of the substantial past efforts using WAI genes suggests that the use of those genes alone will not produce awnless triticale. The reliance on the WAI genes appears to have been an obstacle to achieving a triticale with inhibited awn development comparable to the preferred forage wheats.
The reliance on the WAI genes also appears to have been an obstacle to the development and production of F.sub.1 triticale hybrids having short awns. In triticale, as in many other crops, use of F.sub.1 hybrids could provide tremendous benefits by combining complementary advantages from genetically different parent plants and achieving the added synergistic effect ("hybrid vigor") often associated with combining different genetic types. Triticale is well suited for production of F.sub.1 hybrid seed. In contrast to wheat, for example, triticale has more prolific pollen production and dispersal, more open flowering, and a longer pollination period, all of which facilitate production of hybrid triticale seed. Substantial yield heterosis in triticale provides ample economic benefits to justify the added cost of hybrid seed. By combining the high yields and other advantages of F.sub.1 hybrids with the advantages of short awns, an awnless or short-awn F.sub.1 triticale would have important economic value.